Thermocolor ribbons have long been known and used. In general they may comprise a foil-like support, e.g. of paper, of a synthetic resin or plastic, or the like coated with a melt color in the form of a plastic and/or wax bonded dyestuff or pigment, collectively referred to herein as a coloring agent. Specifically, the meltable color could be a plastic and/or wax bonded carbon black layer.
The melt color is brought to its melting point by means of a thermal printing head (see the aforementioned copending applications) and, upon contact with a receiving substrate, such as writing paper, is transferred to the substrate paper in a pattern determined by the actuation of the head.
Thermal printers and thermal printing heads which can be used for this purpose are likewise known. These heads can utilize pin arrays to build the symbol which is transferred from a plurality of heated points. The symbols can be alphanumeric characters, such as letters or numbers, or other patterns which can be used in graphics or to build up more complex images.
The thermal printing head presses the thermocolor ribbon against the symbol receiving paper and locally heats the melt color to a molten state to effect the transfer to the paper sheet. The oncoming unused thermocolor ribbon may be delivered by a supply spool while the used portion of the thermocolor ribbon can be wound up on a take-up spool.
The thermocolor ribbon can have a plurality of melt colors disposed one adjacent another. Utilizing a combination of the colors blue, yellow, red and black, for example, it is possible to generate colored images. Thermal printers of the aforedescribed type can operate at high speeds, for example, printing an A4 format sheet according to the German Industrial Standard in about 10 seconds without excessive noise generation.
Apart from the thermocolor ribbons described above, there are thermocolor ribbons in which the heated symbol is not generated by the heated printing head but the ribbon is locally heated by resistance heating utilizing a special foil-like carrier. The melt color which is the functional layer in the printing process is brought to the fusion temperature by the electrical heating and a transfer of a symbol pattern can be effected. Such ribbons are referred to as electrothermal ribbons or ETR ribbons.
By and large the printing process described above, if the transfer is made to paper, produces an image or transferred symbol which is not scratch resistant. Such resistance is, however, very necessary in a variety of technical fields. For example, it is essential for the labeling or tagging of tools, workpieces and the like which may be subjected to significant mechanical action and stress.
Such resistance here is defined as the ability of the transferred image to resist mechanical deterioration by rubbing, the movement of sharp edges over the surface and the resistance to abrasive surfaces.